Drilling assembly

ABSTRACT

An assembly for use in drilling in earth borehole using a drill string including a drill bit comprising a first downhole motor having a rotor operatively connected to said drill bit, a second downhole motor distal said first downhole motor, said second downhole motor having a rotor with a passageway therethrough and a bypass valve operatively connected to the second downhole motor, the bypass valve having a first position permitting drilling fluid to flow through said passageway and a second position wherein drilling fluid is prevented from flowing through said passageway.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the priority of U.S. Provisional Application No. 60/899,531 filed on Feb. 5, 2007, the disclosure of which is incorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to drilling earth boreholes and, more particularly, to an assembly for effecting directional drilling of earth boreholes using either coiled tubing rigs or jointed pipe rigs.

2. Description of Prior Art

Directional drilling is widely used in the oil and gas industry whether the drilling be accomplished using coiled tubing rigs or conventional, jointed pipe rigs. As is well known to those skilled in the art, a typical directional drilling system has a drill bit at its bottom end which is rotated by a drill motor, commonly referred to as a “mud motor.” In addition to the drill bit and the mud motor, a typical directional drilling assembly can include an orienting or steering tool, an MWD or LWD tool, drill collars, and a bent sub which can comprise a portion of the housing of the mud motor.

Typically, prior art directional drilling assemblies have comprised a single mud motor, the mud motor supplying, as well known to those skilled in the art, the power to rotate the drill bit.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides an assembly for use in drilling an earth borehole employing a drill string including a drill bit. The assembly can include a first downhole motor having an upper end and a lower end, a first rotor and a first stator, the lower end of the first downhole motor being proximal and operatively connected to the drill bit.

There is also a second downhole motor having an upper end and a lower end, a second rotor and a second stator, the second rotor having a passageway there through and being distal the drill bit. There is a bypass valve operatively connected to the upper end of the second downhole motor, the bypass valve including a valve element which is selectively movable from a first position wherein a drilling fluid flowing through the drill string can flow through the passageway in the second rotor to a second position wherein the drilling fluid is prevented from flowing through the passageway in the second rotor.

In another aspect of the present invention, there is a orienter subassembly forming part of the drill string which can include a bent housing separate from or forming part of the first motor. The second downhole motor, in conjunction with the bypass valve, can be used to induce or stop rotation of at least a portion of the orienter subassembly as required.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of one embodiment of the assembly of the present invention.

FIG. 2 is a schematic, elevational view of a bypass valve used in conjunction with the first or lower motor; and

FIG. 3 is a cross-sectional view taken along the lines 3-3 of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, the assembly of the present invention is shown generally as 10. Assembly 10 is comprised of a bypass valve assembly 12 which would be connected in a suitable manner to coiled tubing or jointed drill pipe, neither of which are shown, which would extend to the surface and be operated either by a coiled tubing injector in the case of coil tubing, or a top drive, rotary table or the like in the case of jointed pipe. Connected to and below bypass valve assembly 12 is the upper mud motor 14 described more fully hereafter. A gear reduction assembly 16 incorporating an anti-torque unit, or a rotary brake unit is connected to the rotor 32 of the motor 14 (see FIG. 2). A tool joint 18 is connected to the gear reduction assembly 16. Connected to tool joint 18 is a bottom hole assembly (BHA) 20 which can comprise suitable drill collars and non-magnetic isolation collars if needed. An MWD logging tool 22 or other formation parameter measuring tool is connected to the BHA 20, an orientation sub 24 being connected to the MWD tool 22. The first or lower motor 26 is connected to the orientation sub 24. As seen, motor 26 has a bent housing as is well known to those skilled in the art. The output of lower motor 26 is operatively connected to a drill bit 28 to effect rotation.

As noted above, the assembly 10 of the present invention is comprised of two mud motors of the positive displacement type. Upper motor 14, as is in the case with most mud motors and as shown in FIG. 2 is comprised of a stator 30 and a rotor 32 positioned in a housing 33, housing 33 having a threaded pin end 35 and a threaded box end 50. Unlike prior art mud motors, rotor 32 has an axially extending passageway 34 which terminates on its upper end in a valve seat 36. Valve assembly 12 comprises a housing 38 defining a bore 40 in which is slidably mounted a valve carrier 42 which carries on its lower end a valve element 44. Operation of valve carrier 42 vis-à-vis reciprocal movement of valve element 44 in bore 40 is via electrical and/or hydraulic power through connection 46, e.g., a wireline, extending to the surface. Valve assembly 12 includes a threaded pin connection 48 which is complimentary to a threaded box 50 in motor 14. It can thus be seen that when valve assembly 12 is connected to motor 16, threaded pin 48 will connect and seal in the threaded box connection 50. Thus, valve element 44 can be selectively engaged and disengaged from valve seat 36 by reciprocating valve carrier 42 in bore 40.

As noted above, the assembly of the present invention uses a novel arrangement of a bypass valve and two, axially spaced motors, an upper motor 14 located proximal the top of the assembly 10 that is used to induce rotation or stop rotation of that portion of the assembly 10 below the motor 14, and a bottom motor 20 which is used to rotate the drill bit 28.

In operation and with bypass valve 12 in the closed position such that valve element 44 is seated in valve seat 36, flow of drilling fluid through passageway 34 is prevented. Accordingly, drilling fluid flowing downwardly through valve assembly 12 into motor 16 will, in the conventional manner, cause rotor 32 to rotate inside stator 30 effecting rotation of the portion of the assembly 10 below motor 14. It will be understood that rotor 32, when the valve assembly 12 is closed, will rotate at a higher speed and hence a lower torque than required to rotate the portion of the assembly 10 below motor 14. Accordingly, to reduce speed and increase torque, gear reduction assembly 16 is employed and has a gearing system designed to provide the desired rotational speed to the portion of the assembly 10 below motor 14. By way of example only, if rotor 32 is operating at 150 rpms, gear reduction assembly 16 may reduce the rotational output of lower motor 16 to 10 rpms or less as desired. It will be understood that when the valve assembly 12 is closed and the remainder of the assembly below motor 14 is rotating, assembly 10 will drill in a straight direction and will continue drilling in a straight direction as long as valve assembly 12 remains closed. In this regard, the portion of the assembly 10 below motor 14 will rotate around an axis generally coincident with the axis of motor 14 meaning that motor 26 and drill bit 28 will be precessing around such axis.

To orient assembly 10 and drill in a desired curved, direction, valve 12 would be opened allowing drilling fluid to pass through passageway 34 effectively bypassing the lobed cavities between rotor 32 and stator 30. Further, closing of bypass valve 12 will cause the rotary brake and/or the anti-torque unit to be engaged. Accordingly, rotor 32 will not rotate and the portion of the assembly 10 below motor 14 will not rotate in any direction. Thus, that portion of assembly 10 can be clocked to a desired, fixed tool face. It will be understood that intermittent opening and closing of valve 12 can be used to orient the assembly 10 to the desired tool face. Once a desired orientation has been achieved and with valve assembly 12 still closed, drilling mud passing through lower motor 26 will cause drill bit 28 to rotate and drill in the direction of the fixed tool face. At this stage, only drill bit 28 will be rotating, the remainder of the orienter assembly 10 will be stationary vis-à-vis rotational movement

It can be seen that the assembly 10 of the present invention, as is conventional, contains a rotating mandrel or tool joint 18 to conventionally connect the desired number of collars, magnetic or non-magnetic, as desired. Additionally, the assembly 10 can contain an MWD tool 22 of the logging tool and an orientation/float sub 24 as required, all of which are conventional and well known to those skilled in the art.

As noted above, at the lower motor 26 of assembly 10 has a bent housing which is connected to the drill bit 28. It is to be understood that upper motor 14 is used to induce or stop rotation of that portion of the assembly 10 below motor 14 as necessary and provides the ability, in combination with the valve assembly 12, to determine the desired orientation. Bottom motor 26, on the other hand, is only used to rotate the drill bit 28.

It will be appreciated by those skilled in the art, that when the orienter assembly 10 is connected to coiled tubing, at no time will bypass valve assembly 12 and motor 14 rotate. It will further be understood that when a straight borehole is being drilled, the entire portion of the assembly below motor 14 will be rotating, as noted above, the bent portion of motor 26 and bit 28 precessing around an axis coincident with an axis passing through motor 14. It will further be understood, that when it is desired to drill a curved borehole, and once the assembly has been clocked to the proper orientation, only drill bit 28 will be rotating, drill bit 28 following the desired tool face direction.

In cases where the assembly 10 is connected to jointed pipe, the description above with respect to the assembly 10 being connected to coiled tubing applies with the exception, that since a jointed pipe string, unlike coiled tubing, can and normally is rotated, motor 14 and bypass valve 12 would be rotating in the borehole since they are fixedly connected to the jointed pipe string.

The anti-torque unit or rotary brake unit has been shown as being incorporated in the gear reduction assembly 16 and below upper mud motor 14, it will be understood that the anti-torque/rotary brake could be above mud motor 14 and more particularly be a part of the bypass valve assembly 12. 

1. An assembly for use in drilling an earth borehole employing a drill string, a drill bit comprising: a first downhole motor having an upper end and a lower end, a first rotor and a first stator, said lower end of said first downhole motor being proximal and operatively connected to said drill bit; a second downhole motor having an upper end and a lower end, a second rotor and a second stator, said second rotor having a passageway therethrough and being distal said drill bit; a bypass valve operatively connected to said upper end of said second downhole motor, said bypass valve being selectively movable from a first position wherein a drilling fluid can flow through said passageway in said second rotor to a second position wherein said drilling fluid is prevented from flowing through said passageway in said second rotor.
 2. The assembly of claim 1, further including an orienter subassembly connected between said first and second motors.
 3. The assembly of claim 1, wherein said bypass valve comprises a valve housing, a valve element carrier reciprocally movable in said valve housing and a valve element connected to said valve element carrier, said upper end of said second rotor having a valve seat engageable by said valve element whereby flow through said passageway can be selectively controlled by movement of said valve element into and out of engagement with said valve seat.
 4. The assembly of claim 1, further comprising a gear reduction subassembly connected to said second rotor.
 5. The assembly of claim 1, further including a logging tool disposed between said first and second motors.
 6. The assembly of claim 1, wherein said first motor has a bent housing. 